Rain water question

[Matt Warner]

Hi all,
After spending the morning cleaning out the leaves from the gutters of the house, and cleaning the water butt, I should now have a pretty clean source of rain water. So next weekend when I do my water change, I am thinking of using some rain water with my regular tap water. Should I get the fish used to rain water by starting with small amounts each week to start with, or will they be ok just using all rain water?
My main concern is stressing the fish from a sudden change in water chemistry.

 

[Tom]

Would likely be a huge jump in hardness from most tap water, so may be best to mix it in gradually.

 

[Matt Warner]

That's what I was thinking too, I usually use about 5 10 litre buckets to do a water change, so I could maybe use 4 tap and 1 rain to start with and gradually increase it. I probably won't use 100% rain water because I won't have anything to buffer the water. So if I use half and half, I'm still saving water, but will have enough hardness to keep the water stable.